The reforming of hydrocarbons boiling within gasoline range without drastically changing their carbon numbers by dehydrocyclization, isomerization, hydrogenation, and/or dehydrogenation has been heretofore accomplished by using catalysts such as platinum-alumina-combined halogen, nickel, cobalt or platinum supported on silica-alumina, and oxides (e.g., molybdenum oxide and tungsten oxide) deposited on silica-alumina. Platinum reforming catalysts, which are preferred, are susceptible to irreversible poisoning, e.g., by sulfur, so that impurities in the feedstock need to be rigorously controlled. See H. Pines, The Chemistry of Catalytic Hydrocarbon Conversions, Academic Press, New York, 1981, pp. 102-104.
An early disclosure regarding the use of carbide catalysts in the reforming of hydrocarbons is U.S. Pat. No. 2,755,228 to V. J. Anhorn et al.
It is known to use transition metal carbide catalysts in the isomerization of hydrocarbons and chemisorbed oxygen on such a catalyst has been indicated as inhibiting hydrogenolysis reactions while leading to an increase in the selectivity to isomerization (See F. H. Ribeiro et al., Journal of Catalysis 130 (1991), 86-105 and 498-513). The presence of oxygen atoms is also said to allow for methyl-shift rearrangements of reactive alkene intermediates (See E. Iglesia et al., Journal of Catalysis 131 (1991), 523-544. The typical way in which oxygen atoms are chemisorbed in such a catalyst system is by the pretreatment of the transition metal catalyst with a source of oxygen. For example, in C. Pham-Huu et al., Journal of Catalysis 143 (1993), 249-261 calcination of a carbide under an air flow at 350.degree. C. for fourteen hours followed by a stabilization period under the reacting mixture (e.g., n-hexane/hydrogen) for six hours at the same temperature is disclosed. U.S. Pat. No. 5,139,987 to M. Ledoux et al. teaches the activation of a heavy metal carbide catalyst under an oxidizing gas stream at temperatures of from 250.degree. C. to 450.degree. C. while maintaining such a temperature for at least three hours followed by cooling to ambient while still under the oxidizing gas stream. More recent U.S. Pat. No. 5,196,389 to D. Dubots teaches the use of oxidation conditions for the pretreatment of the catalyst of from 300.degree. C. to 700.degree. C.
U.S. Pat. No. 4,522,708 to L. Leclercq et al. specifically describes a catalytic reforming process employing reforming catalysts which are based on mixed tungsten and molybdenum carbides.